Disc drive memory systems have been used in computers for many years for storage of digital information. Such information is recorded on concentric memory tracks of a magnetic disc medium, the actual information being stored in the form of magnetic transitions within the medium. The discs themselves are rotatably mounted on a spindle, the information being accessed by means of read write heads supported on a pivoting arm which moves radially over the surface of the disc. The read write heads or transducer must be accurately aligned with the storage tracks on the disc to ensure proper reading and writing of information.
During operation, the discs are rotated at very high speeds within an enclosed housing by means of an electric motor generally located inside the hub or below the discs. One type of motor in common use is known as an in hub or in spindle motor. Such in spindle motors typically have a spindle mounted by means of ball bearing systems to a motor shaft disposed in the center of the hub. However, with the decreasing size of information storage systems, other types of bearings including hydrodynamic bearings are being developed. Useful designs are disclosed in the incorporated applications.
In these types of bearings, a lubricating fluid functions as the actual bearing surface between a stationary base or housing and the rotating spindle or hub and the surrounding stationary portion of the motor. These fluids, either gas or liquid must be sealed within the bearing to avoid loss of the lubricant which would result in reduced bearing load capacity. Otherwise, the physical surfaces of the spindle and housing would contact one another, leading to increased wear and eventual failure of the bearing system. Equally seriously, loss of the seal or failure to control the lubricant level within the bearing system could cause contamination of the hard disc drive with lubricant particles and droplets or outgassing related contamination.
A further critical issue is the need to maintain the stiffness of the hydrodynamic bearing. The stiffer the bearing, the higher the natural frequencies in the radial and axial direction, so that the more stable is the track of the disc being rotated by a spindle on which reading and writing must occur. Thus the stiffness of the bearing in the absence of any mechanical contact between its rotating part becomes critical in the design of the bearing so that the rotating load can be stably and accurately supported on the spindle without wobble or tilt.
A typical prior art grooving pattern is shown in FIG. 1. This pattern was adopted having a constant grooving angle .alpha. which is the angle defined by the groove and the circumference of the cylindrical surface as a constant angle. The pattern provides points of high pressure 10 to seek to optimize the stiffness of the bearing, while providing the desired pumping action of the lubricant to maintain the lubricant surface covered with fluid while minimizing the possibilities of fluid escape. However, because of the sharp angles, at the corners, the grooves are difficult to form, and the tools used to form the grooves wear out quickly.